Short (and useful) python snippets [closed]

Answer 1

I like using any and a generator:

if any(pred(x.item) for x in sequence):
    ...

instead of code written like this:

found = False
for x in sequence:
    if pred(x.n):
        found = True
if found:
    ...

I first learned of this technique from a Peter Norvig article.

Answer 2

To find out if line is empty (i.e. either size 0 or contains only whitespace), use the string method strip in a condition, as follows:

if not line.strip():    # if line is empty
    continue            # skip it

Answer 3

Iterate over any iterable (list, set, file, stream, strings, whatever), of ANY size (including unknown size), by chunks of x elements:

from itertools import chain, islice

def chunks(iterable, size, format=iter):
    it = iter(iterable)
    while True:
        yield format(chain((it.next(),), islice(it, size - 1)))

>>> l = ["a", "b", "c", "d", "e", "f", "g"]
>>> for chunk in chunks(l, 3, tuple):
...         print chunk
...     
("a", "b", "c")
("d", "e", "f")
("g",)

Answer 4

The only 'trick' I know that really wowed me when I learned it is enumerate. It allows you to have access to the indexes of the elements within a for loop.

>>> l = ['a','b','c','d','e','f']
>>> for (index,value) in enumerate(l):
...     print index, value
... 
0 a
1 b
2 c
3 d
4 e
5 f

Answer 5

I actually just created this, but I think it's going to be a very useful debugging tool.

def dirValues(instance, all=False):
    retVal = {}
    for prop in dir(instance):
        if not all and prop[1] == "_":
            continue
        retVal[prop] = getattr(instance, prop)
    return retVal

I usually use dir() in a pdb context, but I think this will be much more useful:

(pdb) from pprint import pprint as pp
(pdb) from myUtils import dirValues
(pdb) pp(dirValues(someInstance))

Answer 6

Emulating a switch statement. For example switch(x) {..}:

def a():
  print "a"

def b():
  print "b"

def default():
   print "default"

apply({1:a, 2:b}.get(x, default))